Along the two long sides of such vehicles as lorries, there is a free space between the front wheel sets and rear wheel sets and under the part of the platform of the vehicle that protrudes from the chassis or the frame work constituting a risk factor in regard of road safety in so far that other vehicles, such as private cars, two-wheelers and the like, may drive into the same and become wedged up under the projecting platform section. In this connection, the platform section may give rise to serious personal injuries. In order to avoid such underrun accidents, the vehicles may be provided with particular underrun protections that essentially extend in flush with the long sides of the platform or addition in order to cover most of the space between the front and rear wheels. However, previously known underrun protections are permanently immovably fixed in relation to the vehicle chassis, more precisely by the covering sheet unit being stiffly united to a fastening unit, which is in turn stiffly connected to the chassis, e.g. by means of welded or bolt joints. The fact that the underrun protection is fixed in a given position makes it difficult or impossible to practically utilize the storage box or storage boxes that usually are mounted on the chassis in the area immediately under the platform. Another shortcoming of the known underrun protections is that the same are not suitable for exposing commercial and/or information messages, in spite of the fact that the same are well visible, for instance from the side of the vehicle.